Elimination of disturbing oscillations in high-frequency systems



Oct. 8, 1929 ELIMINATION OFDISTURBING OSCILLATIONS" IN HIGH FREQUENCY SYSTEMS K. SQ-MID? ET AL, 1,730,903

Filedimay 20, 1926' Invaders:-

63" ,t cfimidzfi and.

Matte r- Hahneman n Patented a. 8,1929

KARL SCHMIDT, OF BERLINJJICZETENRAIJ'E.

AND WALTER HAHNEMANN, .OF BERLIN:

' TEMPELHOF, GERMANY, ASSIGNORS r0 0. LORENZ nx'rmnensnmscnar'r, or

BERLIN, GERMANY ELIMINATION OF DISTURBING OSCILLA TIONS IN HIGH-FREQUENCY SYSTEMS Application filed May 20, 192.6, Serial No.

The present inventiui relates to radio transmission systems, and has for its objectthe elimination either in the transmitting or receiving circuits of higher harmonics, side frequencies or other disturbing waves. I 'f According to this invention the objectionable frequencies are eliminated byAthe insertion, in any circuit in which such frequencies appear'in conjunction with the operative frequency, of an iron core choke coil- (which may be called a filter transformer) with a seci has very small magnetic ondary coil short circuited by acombination of-inductance and capacity in. series. This capacity and inductance circuit is tuned to the operating frequency and acts as an acceptorcircuit with the result that the choke coil op:

lerates in the manner of a short circuited transformer at the operative frequency, that is, it

held and therefore the losses almost disappear, while at all other frequencies, since a large impedance is presented by the primary winding of the transformer, a magnetic embodiment of our a coupling field would be present and the consequent losses willact to choke off the undesired frequency. In this way the impedanc'e of the combination at the,operating frequency isnegligibly small,' but retains its full value at the undesired frequency.

In order that the invention may be clearly understood and readily carried into effect it. will now be described more fully with reference to the accompanying drawingwhich illustrates diagrammatically three applications of the invention, I

Fi ure 1 is a circuit diagram of a preferred invention.

Figure 2 is a modificationof Figure l in which an auto-transformer replacesthe trans former of Figure 1 and 4 r Figure 8'is a circuit diagram by way of example, of in-application of the invention to' areceiver circuit.

Figure 1 shows a transmission circuit. employing a static frequency transformer Tr in which higher harmonics and side frequencies are highly undesirable.

According tolthis invention there is connected in series with a tuning capacity C and device K for transmitting the oscillations tothe aerial a filtertransformer 110,364, and in Germany May 27, 1925.

F constituted by an iron core provided with two windings w and to. A variable capacity I G8, which represents a secondary tuning member in series with a self-inductance L is connected in circuit with the-winding 'w and is intended totune' the circuit of this winding to resonance with the operative waves. In the circuit T1, C, w in addition to the desired f operative waves, there is a series of higher harmonics and side, frequencies; these meet, in the primary winding w of the filter transformer, with such a high resistance loss that they become uniformly for the operative wave, the primary winding acts as a low resistance path, since, owing to the high resonance current produced inthe extinguished, whilst, 4

secondary circuit-10 L, C8, the field of the operative waves in. transformer F is annulledcand in that -the selfinduction, and therefore the iron losses, are practically oancelled,being reduced to that due to leakage. This can in turn be reduced or minimized by using a transformer as fares possible without leakage, for instance, as shown in the 'drawing,.one with an annular. iron core. By making the self-in ductanee L large with respect to capacity C8 mostly be the case in practice on account "the freedom from leakage of such an arrangement,

. Figure 3 shows by way of example the apcircuit of the transformer grid circuit of the valve, whilst disturbing the iron core of the filter the damping of thesecondary circuit may be i plication of the invention to a receiving circuit, the secondary F beingtuned to the wave tobereceived, "which is thus solely operative in'afiecting the waves are suppressed, Alternatively, an auto-transformer could be used or the trans former couldb'einserted in the aerial circuit instead of in the secondary circuit.

, It is a well-known thing in the art of elec- I trical englneering that ashortcircuited transformer presents a very low. lmpedance 1n the circuit and therefore W111 pass a considerable current without any rise of voltage at the terminals. This is especially true withiron amount of current could surge through the secondary, and the effect on the primary core transformers: arranged'in a ring shapei wouldbe the same as if the secondary were .where the stray. fields; and the consequent leakage inductance are negligible. -'Asthe impedance of the secondary "ClIClllt is increased the impedanceof the primary circuit? varies correspondingly until at open circuit" the-primary impedance is a. maximum corresponding to the magnetizing current of the transformer, and taking practically the full}; available voltage. I I

In this invention this'well-known function of a'transformer is taken advantage of for the purpose of permitting the desired frequency to pass through and for blocking off all of the undersired frequencies. The secondary winding instead of being short circuited is con-g" nected to an inductance and a condenser which are tuned to the desired frequency. I As a result the secondary circuit presents an extremely low impedance at the desired frequency, I corresponding to an impedance :of

I such a seriesconnection at the instant when the reactance of the inductance is equal to the reactanceof the condenser.

' On the other hand, v frequencies the re'actance of the condenser does not cancel thevreactance of the inductancefand therefore there is an appreciable imaccompanied by a corresponding magnetic a magnetic flux,

flux through the iron coreof the transformer and such a magnetic flux will produce considerable losses. "Thus, in addition to the blocking effect of the choke coil there is also an absorbingefi'ect, .due to the losses of the ironcore. v

Again referring to the mode of operation with the desired or with the operative frequency; on account of the very low secondary impedance, the primary impedance is also negligible, ,no voltage is found at the terminals, and therefore there is no necessity for a hence the losses at the operaare non-existent, or very small.

tive frequency J Further insight into theoperation of the device can be obtained by considering What would happen if the secondary of a transformer were connected to the terminals of a condenser. Obviously, if the condenser were exceedingly small a very minute amount of current passing through the secondary would be suflicient to charge the condenser to full A. C. potential and the effect on the primary would be approximately the same as if the secondary were on open circuit. Ifthe secondary were connected to the terminals of acondenser of extremely large size, a large annet with very slight impedance in the pri-v the 'placing of a conmary'. In other words, denser alone in the secondary wouldnot permit sharp tuning to agiven desired frequency unless the transformer had large 'inherent leakage inductance. Hence the inclusion of an inductance along with the condenser inv the secondary circuit as described and illustrated.

'What we claim is: a

J 1. An apparatus for the elimination of higher harmonics, side frequencies or other disturbing waves in a radio transmission circuit comprising the primary of an iron cored transformer inserted in the circuit in which such waves exist in conjunction with the operative series of oscillation and electrical means associated with the secondary coil of said transformer whereby the circuit of'said secondary coil may be tuned to react on the primary to renderits impedance a minimum with respect to the operating frequency.

disturbing waves in radio transmission systems, comprising'a primary coil of a transformer inserted in a circuit in which such waves exist in conjunction with the operative series of oscillations, aniron core for said coil, a secondary coil for said transformer and' shuntedby a variable capacity in series with an in inductance-coil the thus formed secondary circuit being tuned to react on said primary to make its lmpedance a minimum 1n respect to the operative osclllations.

3. An apparatus for the elimination ofhigher harmonics, side frequencies, or other disturbing waves in radio transmission systems, comprising a coil wound on a closed iron core inserted in the circuit in which such waves existin conjun'ctionwith the operative series of oscillations and comprising a capacity in series with an inductance coil connected in parallel with a portion of said coil, the thus formed shunt circuit being tuned to react on said coil to make its impedance a minimum in respect to the operative oscillations. p 4. An apparatus for eliminating objectionable frequencies from a radio circuit comprising'a transformer, a primary for said transformer forming part of said radio circuit, an

in the secondary tuned to a predetermined frequency whereby the magnetic field producedin said iron, core by the predetermined frequency is destroyed and consequent losses and impedance at all other frequencies are produced.

5. An apparatus -for eliminating side frequencies from a radio circuit comprising a choke coil in the circuit, an iron core in the choke coil, a second coil tionship to the choke coil through the iron core and a-capaoity in series with an induc- "tance in circuit with said second coil toperinitoscillations of operating frequency to pass through said choke coil vithout impedance voltage drop or loss of energy in said choke coil.

6. An apparatus for reduction of undesirable frequencies comprising a closely coupled transformer, a primary of said transformer forming part of a radio frequency circuit, and a tuned combination of capacity and inductance in series in the secondary circuit of said transformer to produce an equivalent low impedance of the transformer primary at the operating frequency and a relatively high impedance at all other frequencies.

7. An apparatus for the elimination of objectionable frequencies in a radio circuit, comprising an iron core inductance coil inserted in said circuit and means including a tuned circuit in inductive relation With said inductance coil for bypassing the operating frequency and preventing it from producing an appreciable voltage drop through said inductance coil.

8. An apparatus for the elimination of objectionable frequencies in a radio circuit, comprising an iron core inductance coil inserted in said circuit, a secondary Winding of said core, and a resonant circuit containing a capacity and an inductance coil in series connected to said secondary for tuning said secondar "so as to produce a minimum imped-' ance at said coil in respect to the operating frequency.

In testimony whereof We have afiixed our signatures. I

KARL SCHMIDT. \VALTER HAHNEMANN.

having inductive rela- 

